Method for monitoring the transmission quality of connections in mpls networks

ABSTRACT

The invention relates to a low-effort monitoring method of the transmission quality of connections in MPLS networks. Specially configured MPLS-OAM packets (MPLS-OAM-LAV packets) are defined and are periodically inserted into the traffic flow of user data packets at the source of a connection or a partial section of a connection, said MPLS-OAM-LAV packets being distinguishable from other MPLS-OAM packets and the MPLS packets carrying user data by a special mark. The information part of the MPLS-OAM-LAV packets contains a field receiving the number of MPLS packets that have been sent within a given period of time. Said tally is read out at the reception end (acceptor) and is compared with the number of actual packets received for said connection within the given period of time. The result serves as a criterion for lost and/or erroneously added packets.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/DE03/01336, filed Apr. 24, 2003 and claims the benefit thereof.The International Application claims the benefits of German applicationNo. 10219152.2 DE filed Apr. 29, 2002, both of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method in accordance with the claims.

BACKGROUND OF INVENTION

In the prior art OAM (Operation and Maintenance) functionality is to beseen as a significant element of the operation of public communicationsnetworks. It supports the quality of the network performance whilesimultaneously reducing the operating costs of the networks. It makes asignificant contribution, especially with regard to the Quality ofService (QoS) of the information transmitted. Strategies in respect ofOAM functionalities have already been proposed for SONET/SDH as well asfor ATM networks.

The OAM functionality allows the operator of a communications network tofind out at any time whether the guaranteed quality-of-service levels(Service Level Agreement) for a connection are being adhered to. To beable to do this, the operator must also know the availability ofexisting connections (connection “up” or “down”), as well as the timedelay for the transfer of the information (delay, delay variation),the—if necessary averaged—deviation from the otherwise normal gapbetween two information transfers (delay jitter) or the number of itemsof information not even allowed to be transferred (blocking rate,error).

If for example a connection fails, the fault must be determinedimmediately (fault detection), localized (fault localization) and theconnection must also be able where necessary to be diverted to a standbyroute (protection switching). This enables both the traffic flow and thebilling procedures in the network to be improved. MPLS networks arecurrently proposed for transmissions of information in the Internet. InMPLS (Multiprotocol Label Switching) networks information is transmittedby means of MPLS packets. MPLS packets are of variable length and eachfeature a header part and an information part. The header part is usedto accommodate the connection information whereas the information partserves to accommodate payload information. IP packets are used aspayload information. The connection information contained in the headerpart is embodied as an MPLS connection number. This number is only validin the MPLS network however. This means that when an IP packet from anInternet network penetrates into the MPLS network (FIG. 1), this packetwill be prefixed with the header part valid in the MPLS network. Thisheader contains all the connection information which specifies the routeof the MPLS packet in the MPLS network. If the MPLS packet leaves theMPLS network, the header part is removed again and the IP packet isrouted onwards in the subsequent Internet network in accordance with theIP protocol. MPLS packets are transmitted unidirectionally.

FIG. 1 starts off from the typical assumption that information will forexample be routed from a subscriber TLN1 to a subscriber TLN2. Thesending subscriber TLN1 is connected in this case to the Internetnetwork IP through which the information is routed in accordance with anInternet protocol, such as the IP protocol. This protocol is not aconnection-oriented protocol The Internet network IP features aplurality of routers R which can be intermeshed. The receivingsubscriber TLN2 is connected to a further Internet network IP. An MPLSnetwork is inserted between the two Internet networks IP, through whichpacket-oriented information is switched in the form of MPLS packets.This network also features a plurality of intermeshed routers. In anMPLS network these can be so-called Label Switched Routers (LSR).

In MPLS networks the guarantee of Quality of Service (QoS) assumes majorsignificance. In this case knowledge of the packets which are lost orincorrectly inserted during transmission has an important role to playfor the network provider (transmission quality, performance monitoring),since on the basis of this information they can provide users with thecorresponding connections. However the prior art does not contribute inany way to resolving this problem.

SUMMARY OF INVENTION

The object of the invention is to demonstrate a way in which informationabout packets lost or incorrectly inserted during transmission can bemade available with minimal effort in MPLS networks.

The object of the invention is achieved by starting from the featuresspecified in of the claims by the identifying features.

Especially advantageous in the invention is the provision ofspecifically embodied MPLS-OAM packets, which are inserted into thetraffic stream of payload data packets. In addition to the mark oridentification in the header identifying the packet as an MPLS OAMpacket (to distinguish between the MPLS OAM packets and MPLS packetscarrying payload data) a further identification is required. The packetsdefined in this way (identified below as MPLS-OAM-LAV packets) are usedfor performance monitoring of an MPLS connection (MPLS Label SwitchedPath) while in the Information part of the MPLS-OAM-LAV packet a fieldis provided to accept the number of the MPLS packets sent per intervalof time. On the receive side (sink) this count value also transmitted isread out and compared to the number of packets actually received forthis connection within the specified time interval, with the resultacting as a criterion for lost and/or incorrectly inserted packets.

Advantageous developments of the invention are specified in thedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained below in more detail using an exemplaryembodiment.

The diagrams show:

FIG. 1 the basic circumstances in an MPLS network

FIG. 2 an end-to-end connection between two subscribers

FIG. 3 the circumstances in the packet header and in the informationpart of an MPLS-OAM packet

DETAILED DESCRIPTION OF INVENTION

FIG. 2 shows a connection (Label Switched Path, LSP) between twosubscribers TLN1, TLN2. This connection is routed via a plurality ofnodes N1 . . . N4, which means that a plurality of connection hops(Label Switched Hop) are defined. The nodes N1 . . . N4 should beembodied as routers, LSRs of an MPLS network. After a successfulconnection setup information is now flowing between subscriber TLN1 andsubscriber TLN2 comprising a plurality of MPLS packets carrying payloaddata information. MPLS-OAM packets can be inserted into this MPLS packetflow (Inband LSP). By contrast connections are defined via whichexclusively MPLS-OAM packets are routed (Outband LSP). Basically inbandMPLS-OAM packets are useful for logging LSP connections on an individualbasis. In a number of cases it can be advantageous to define anout-of-band MPLS-OAM packet flow. One example of this is the MPLS groupprotection switching.

To be able to distinguish between MPLS-OAM packets and MPLS packetscarrying payload data, the MPLS-OAM packets are marked. The specialmarking mechanisms are shown in FIG. 3 and are described later ingreater detail. The sequence of a number of MPLS-OAM packets defines anMPLS-OAM packet flow. Basically 3 different types of MPLS-OAM packetflows can exist simultaneously for an LSP connection:

End-to-end MPLS-OAM packet flow. This is used in particular if there isOAM communication between a source and a sink of an LSP connection. Itis formed from MPLS-OAM packets which are inserted into the payload datastream in the source of the LSP connection and are removed again at thesink. The MPLS-OAM packets can be recorded and monitored along the LSPconnection at the Connection Point CP without the need for interventioninto the transmission process (passive).

One of the end-to-end defined MPLS-OAM packet flows is the MPLS-OAMpacket flow type A. It is used in particular if there is OAMcommunication between the nodes which delimit the type A connectionsegment (FIG. 2). One or more type-A MPLS-OAM segments can be defined inthe LSP connection, but they can neither be interleaved nor can theyoverlap with other segments of type A.

Finally, of the two types of packet flow specified below, type-BMPLS-OAM packet flow is identified. It is used in particular if there isOAM communication between the nodes which delimit the type B connectionsegment (FIG. 2). One or more type-B MPLS-OAM segments can be defined inthe LSP connection, but they can neither be interleaved nor can theyoverlap with other segments of type B.

Basically an MPLS-OAM packet flow (end-to-end, type A, type B) is madeup of MPLS-OAM packets which are inserted at the start of the sectioninto the payload data stream and removed from this stream again at theend of the segment. They can be recorded and processed along the LSPconnection at the Connection Point CP without the need for interventioninto the transmission process. Each Connection point CP in the LSPconnection including the sources and sinks of the connection can beconfigured as MPLS-OAM source or MPLS-OAM sink, in which case theoutgoing MPLS-OAM packets from an MPLS-OAM source are preferably to beconfigured as “upstream”.

Before MPLS-OAM packets (end-to-end, type A, type B) are transmittedover the MPLS network, the end points (source, sink) of the associatedMPLS-OAM segment must be defined. The definition of source and sink foran MPLS-OAM segment is not necessarily set for the duration of theconnection. This means for example that the segment involved can bereconfigured via fields in the signaling protocol.

For each LSP connection interleaving of the segmented MPLS-OAM-packetflow (type A or type B) within an end-to-end MPLS-OAM packet flow ispossible. In this case the Connection Points CP can simultaneously besource/sink of a segment flow (type A or type B) and also of theend-to-end MPLS-OAM packet flow.

The MPLS-OAM packet flow (segment flow) of type A is functionallyindependent of that of type B with regard to the insertion, removal andthe processing of the MPLS-OAM packets. In general it is thus possibleto interleave type-B MPLS-OAM-packets with those of Type A and viceversa in the case of interleaving a Connection point CP can thus alsosimultaneously be source and sink of an OAM segment flow of type A andof type B.

The overlapping of the type A segments with those of type B is possibledepending on the network architecture. For example in the case of apoint-to-point-network architectures segments of type A can overlap withthose of type B. Both segments can operate independently and will thusnot influence each other in any way. In MPLS protection switchinghowever the overlapping can lead to problems.

The MPLS-OAM packets can be distinguished from MPLS packets carryingpayload data by using one of the EXP bits in the MPLS packet header.This method in particular provides a very simple method ofdistinguishing between packets. This bit can be checked in the sink ofan MPLS-OAM segment or at the Connection points CP to filter outMPLS-OAM packets before further evaluation is undertaken.

Alternatively one of the MPLS label values) No. 4 to No. 15 can be usedas an identifier in the header part of the MPLS packet. These MPLS labelvalues are reserved by the IANA. In this case the next identification inthe stack of the assigned LSP connection must indicate what the OAMfunctionality is used for. This approach to a solution is rather morecomplex to implement since the hardware in the OAM sink and theConnection points CP needs two MPLS stack entries for each MPLS-OAMpacket. Naturally processing must take place in real time, i.e. in theConnection Points CP the OAM packets must be inserted back into the flowwhile retaining the sequence. This is absolutely necessary to ensurecorrect performance monitoring results in the OAM sink.

For verification of the availability of an MPLS-LSP connection (referredto below as the MPLS-LAV function, MPLS-OAM-LAV packets are defined.They are inserted into the flow of the payload information (in-bandflow) and are assigned to a specific LSP connection. Thus theavailability of an LSP connection can be determined on an end-to-endbasis or a segmented basis. For this purpose an MPLS-OAM-LAV packet isinserted periodically per time interval (e.g. per second) at the sourceand is monitored periodically per time interval (e.g. per second) at thesink for its arrival. If, after a predefined time (of a number ofseconds for example) and if necessary multiple checks (e.g. 2 to 3times) no MPLS-OAM-LAV packet has been received at the sink, the LSPconnection is declared as not available (LSP=“down” or “unavailable”).in the case of the non-available LSP connection further periodic checksare made at the sink for the arrival of the MPLS-OAM-LAV packet, and if,after a predefined period (of several seconds) this is received at thesink again, the connection is declared as available again.

The MPLS-LAV function can be activated simultaneously on an end-to-endbasis or segmented basis for each LSP connection at any interface CP ornetwork element. Activation and deactivation is just as possible usingsignaling procedures as it is using manual configuration via networkmanagement. The feature can be activated at any time, that is eitherduring connection setup or afterwards.

If a segment is monitored it is first necessary to define the limits ofthe segment involved with the assigned LSP connection. This is generallydone by determining source and sink. After this the MPLS-LAV functioncan then be activated. It must however be inactive if the limits of asegment are to be changed or the segment is to be deleted, which ispossible at any time.

The advantage of the MPLS-LAV function lies in its ability to checkwhether the quality of service parameters in the service level agreementof the LSP connection involved have also been adhered to. Theavailability status is especially of interest here, i.e. whether the LSPconnection is available (LSP=“up” or “available”) or not (LSP=“down” or“unavailable”). This allows the failure of an LSP connection (SignalFail Situations) to be determined. In this case MPLS protectionswitching can be initiated or an alarm generated, which is forwarded tothe network operator if necessary.

The availability status of the LSP connection (LSP=“available”,LSP=“unavailable”) is now taken as the basis for further information.Thus the availability status is an indication for the occurrence of thefailure of a connection (Signal Fail Situation). In the case ofnon-availability a “Signal Fail” signal is activated. in the case ofavailability of the connection this signal is deactivated. With the aidof this signal protection switching requests (MPLS Protection Switching)or alarms can then be initiated. Furthermore the location of theunderlying network fault can be determined as part of diagnosticmeasures.

As an additional function for the monitoring function (MPLS-LAVfunction) a further purely passive monitoring function (non-intrusivemonitoring function) can be provided. With this function theMPLS-OAM-LAV packets are only read during the monitoring procedure butare not modified (non-intrusive). They can be determined at each of theConnection Points CP along the MPLS-OAM-LAV traffic flow on anend-to-end basis or segment basis by the content of the MPLS-OAM-LAVpackets passing the Connection Point CP being processed withoutcharacteristic values such as the content of the packets for examplebeing changed. Monitoring is also undertaken end-to-end, i.e. in thiscase individual connection segments of the overall connection arechecked. In this case passive monitoring includes that samefunctionality as that described for the MPLS-LAV function.

The advantage of the passive monitoring function is to be seen in faultlocalization. With this a step-by-step method can be implemented whichallows the parts of the LSP connection which are interrupted to bedetermined. The signal degrade can thus be determined.

The MPLS-LAV function further forms the basis for monitoring thetransmission quality (performance monitoring). In this case the functionwhich monitors the transmission quality (called the PM function below),is to be seen as a subfunction of the MPLS-LAV function.

The function is used to monitor the transmission quality of a connectionon an end-to-end basis or a segment basis. In this case the number ofMPLS-LAV packets which are lost per interval of time during transmissionplays as great a role as the number of packets inserted incorrectly. Aninterval of 1 second can be used as a time interval for example(one-second interval). For this purpose the MPLS-OAM-LAV packagecontains a special field for accommodating a packet counter.

Transmission quality is now monitored by initially counting in thesource the number of MPLS packets carrying payload data sent which aretransmitted per second for the LSP connection involved. The valuedetermined in this way is transmitted to the sink where it is comparedto the status of a further counter, in which the number of MPLS packetscarrying payload data which have arrived at the sink is recorded. Bycomparing the two values the number of packets lost during thetransmission or the packets incorrectly inserted can be determined.

The PM function can only be activated if the (associated) MPLS-LAVfunction is active. If this is the case for a specific LSP connectionthe function can be active or inactive depending on requirements. The PMfunction can also be activated and deactivated using signalingprocedures as it can be alternatively by manual configuration.

The PM function is used to determine and whether negotiated (ServiceLevel Agreement), guaranteed quality of service (QoS) of the assignedLSP connection has also been maintained. This includes for example therequirements with regard to a error performance. Furthermore it can bedetermined whether the throughput guaranteed for the connection hasactually been maintained by a network.

The PM function can also be used to identify it the degradation of asignal (Signal Degrade) for an LSP connection. In this case MPLSprotection switching can be initiated as a result. As an alternativealarm can also be generated which is routed to the network operator forexample. As a further application MPLS Traffic Engineering can beprovided to enable overload situations in the network to be determined.

When the PM function is active a free running at counter in the saucecounts the number of MPLS Packets carrying payload data which were sentfor a corresponding LSP connection. In this case MPLS packets carryingpayload data are taken to mean all packets which are not marked as OAMpackets. The counter can for example be embodied as a 16-bit counter(free running, modulo 65536). Each time that an MPLS packet is insertedinto the MPLS traffic flow of the LSP connection involved (e.g. persecond) the current value of the counter is written into thecorresponding field of the MPLS LAV packet. This means that on the sendside (Source) the difference between two consecutive counter statescorresponds to the number of MPLS packets carrying payload data whichhave been transmitted between two MPLS-OAM-LAV packets transmittedimmediately after one another.

When the function is active a further free running counter in the sinkcounts the number of MPLS packets carrying a payload data which arrive(for this LSP connection). This counter is also embodied as a 16-bitcounter (free-running, modulo 65536). Each time that an MPLS-OAM-LAVpacket is received for the relevant LSP connection (e.g. per second),the following calculations are made in real-time processing (i.e. withinthe transmission time of an MPLS packet carrying the payload data):

Initially in the first calculation step the difference is formed betweenthe current counter status (after determining of the number of MPLSpackets arriving) and the counter status shown by this counter onevaluation of the last MPLS-OAM-LAV packet. The result corresponds tothe number of MPLS packets carrying payload data which arrived duringthe one-second interval for this LSP connection.

This is then followed in a second calculation step by reading at thecounter status transmitted as well in the MPLS-OAM-LAV packet, andsubtracting it from the value of the MPLS-OAM-LAV packet which arrivedpreviously. The result corresponds to the number of MPLS packetscarrying user data which have been sent in the source for this LSPconnection.

The difference between two calculations corresponds to the number ofpackets lost during the last one-second interval for the LSP connectioninvolved (assuming that more packets were sent than were received). Thisresult will be stored for this time interval. If more packets havearrived than were sent it is assumed that packets were incorrectlyinserted somewhere into this LSP connection during the transmission. Afree-running one-second counter in the sink then initiates furtherprocessing.

If the status of the associated LSP connection is “down” or“unavailable” activation of the PM function is suppressed until thestatus of this connection is again “up” or “available.

If the information contained in an MPLS-OAM-LAV packet regarding the PMfunction is lost no major problems should be expected. The packetreceived next with information and relating it to the PM is then simplyevaluated and the result is applied to the two-second interval.

With a 16-bit counter—as described above—connections with a throughputof 10 Gbit/sec (corresponding to approximately 300 million IP packetsper second) and packets losses can be precisely calculated to at leastthe power of 10-4. This assumes IP packets with the smallest possiblesize. For higher packet losses the results can be more imprecise inwhich case it is however likely that under these circumstances theconnection will be interrupted (Signal Fail) and declared as unavailablein which case the performance monitoring results are invalid in anyevent.

If both the loss and also the incorrect insertion of packets of occursdirectly consecutively the results will partly balance each other out.It can however be assumed here that this does not represent a usualsituation in normal operation.

The results as regards the loss rates or incorrect insertion of packetsper one-second interval are taken as a basis for further calculations:

It is thus possible with this information to determine whether a signaldegrade situation has occurred. If this is the case MPLS protectionswitching can be initiated for example. Furthermore the results for aone-second interval can be accumulated into a 15-minute interval. Thisenables the appropriate statements to be made for a 15-minute interval.These are stored and if necessary directed to network management.Further intervals such as for example 24-hour intervals are alsopossible.

Further the transmission quality of the connection or of a segment ofthe connection can be monitored in any network equipment lying betweenthe source and the sink. With

-   -   the information about the transmission quality of the MPLS        connection in any MPLS network equipment lying between the        source and the sink it is also possible to locate the underlying        network faults within the framework of diagnostic measures.

1-7. (canceled)
 8. A method for connection-oriented transmission ofvariable-length packets over a connection, the connection including aplurality of connection sections, comprising: marking some of thepackets; supplying an identifier and a count value to some of the markedpackets; entering a number of transmitted packets within a specifiedtime interval into the count value, the count value entered at a sendingside; receiving the count value; comparing the count value with a numberof packets actually received for the connection within the specifiedtime interval; and using the compared results as a criterion fortransmission discrepancies, the transmission discrepancies selected fromthe group consisting of lost packets, inserted packets, and acombination thereof, wherein a link is selected from the groupconsisting of the connection and connection sections.
 9. The method asclaimed in claim 8, wherein the variable-length packets are transmittedvia a multiprotocol label switching method.
 10. The method as claimed inclaim 9, wherein the variable-length packets are MPLS packets, themarked packets are MPLS OAM packets, and the MPLS OAM packets includingthe identifier are MPLS OAM LAV packets.
 11. The method as claimed inclaim 10, wherein the MPLS network is monitored via the MPLS-OAM-LAVpacket, the MPLS-OAM-LAV packets are marked as a segment MPLS-OAMtraffic flow and the MPLS-OAM-LAV packets are transmitted in theconnection segment that is identified as an OAM segment.
 12. The methodas claimed in claim 10, wherein an alarm indicating that a transmissionquality is adversely effected is generated and forwarded to a handlerselected from the group consisting of network operator, MPLS protectionswitching procedure and combinations thereof, when a number of thetransmission discrepancies of the link exceeds a present thresholdvalue.
 13. The method as claimed in claim 12, wherein information of thetransmission quality being adversely effected is forwarded to a networkmanagement system where the information is processed and stored toprovide a network operator with transmission quality statistics of thelink.
 14. The method as claimed in claim 8, wherein a transmissionquality of the link is monitored in any network equipment lying betweena source and a sink
 15. The method as claimed in claim 14, wherein anetwork control is selected from the group consisting of a networksignaling and network management.
 16. The method as claimed in claim 15,wherein a monitoring of the transmission quality of the link can beactivated at the source and the sink by control sequences initiated viaa network control.
 17. The method as claimed in claim 15, wherein amonitoring of the transmission quality of the link can be deactivated atthe source and the sink by control sequences initiated via a networkcontrol.
 18. A mutiprotocol label switching network, comprising: aconnection maintained over a plurality of nodes implemented as labelswitched routers, the connection including a connection section; aplurality of variable length MPLS packets; a mark included in some ofthe MPLS packets; an indicator included in some of the marked MPLSpackets; a send count value containing a count of the MPLS packetstransmitted within a specified time interval, the count value includedin some of the MPLS packets; and a receive count value containing theactual number of MPLS packets received, a transmission discrepancydetected by comparing the send count value in a received MPLS packetwith the receive count value, wherein the transmission discrepancy isselected from the group consisting of lost MPLS packets, inserted MPLSpackets and a combination thereof, wherein a link is selected from thegroup consisting of the connection and connection sections.
 19. Thenetwork as claimed in claim 18, wherein an alarm indicating that atransmission quality is adversely effected is generated and forwarded toa handler selected from the group consisting of network operator, MPLSprotection switching procedure and combinations thereof, when a numberof the transmission discrepancies of the link exceeds a presentthreshold value.
 20. The network as claimed in claim 18, whereintransmission quality information is forwarded to a network managementsystem providing transmission quality statistics of the link.
 21. Thenetwork as claimed in claim 18, wherein a transmission quality of thelink is monitored by a sink.
 22. The network as claimed in claim 18,wherein a transmission quality of the link is monitored by a source. 23.The network as claimed in claim 18, wherein a transmission quality ofthe link is monitored by network equipment between a sink and a source.24. The network as claimed in claim 18, wherein monitoring thetransmission quality of the link may be activated.
 25. The network asclaimed in claim 18, wherein monitoring the transmission quality of thelink may be deactivated.